Silica films, such as SiO2, are used in the microelectronics industry as dielectrics. A dielectric is described by its dielectric constant, more commonly known as the k-value of the dielectric. Dielectrics are used to isolate metal lines or layers from one another. Using a dielectric with a low dielectric constant helps to lessen crosstalk, the undesired capacitive or inductive interaction of one part of the circuit to another. As device density on integrated circuits increases, the metal lines become smaller, and the distance between metal layers decreases. As device geometries decrease, crosstalk effects become significant. Crosstalk effects can be reduced by lowering the k-value of the dielectric. Current technology uses dielectrics with a k-value between 2.5 and 4.0.
Silica has a dielectric constant of about 4.0, which is too high to be useful for next generation integrated circuits. Since air has a dielectric constant of 1.0, one way to lower the dielectric constant of silica is to incorporate voids or pores into the silica. There are several drawbacks to using this approach in an integrated circuit manufacturing process. First, porous dielectrics are generally not mechanically stable enough to support subsequent polishing operations. Additionally, the porous dielectric may allow transport of metal through the dielectric layer.